When you consider the utter vastness of space, it isn't hard to accept that, somewhere out there, extraterrestrial life probably exists. That being said, one can just as soon reason that the Universe is so immense, the odds of us actually finding evidence for the existence of alien organisms are probably pretty slim. Given the mind-boggling hugeness of the cosmos, where would we even begin looking for signs of life?

Well... why not the Moon?

As we've mentioned before, there are a few obvious answers to the question of where to look for evidence for the existence (or potential for existence) of extraterrestrial life:

Earth-like exoplanet, Kepler-22b? Hell yeah (as soon as we figure out how to make the 600-light-year trip).

But the Moon? It's certainly close, but, Transformers notwithstanding, it doesn't exactly spring to mind when you ruminate on places that could be harboring signs of alien life.

And yet, in a paper published in the latest issue of Acta Astronautica, researchers Paul Davies and Robert Wagner of Arizona State University present a pretty compelling argument for going alien-relic hunting on the Moon. The researchers write:

The Search for Extraterrestrial Intelligence (SETI) has a low probability of success, but it would have a high impact if successful. Therefore it makes sense to widen the search as much as possible within the confines of the modest budget and limited resources currently available. To date, SETI has been dominated by the paradigm of seeking deliberately beamed radio messages.

However, indirect evidence for extraterrestrial intelligence could come from any incontrovertible signatures of non-human technology [the researchers mention probes sent to our galaxy by alien civilizations as an example]. Existing searchable databases from astronomy, biology, earth and planetary sciences all offer low-cost opportunities to seek a footprint of extraterrestrial technology... [databases like] the photographic mapping of the Moon's surface by the Lunar Reconnaissance Orbiter (LRO) to 0.5 m resolution. Although there is only a tiny probability that alien technology would have left traces on the moon in the form of an artifact or surface modification of lunar features, this location has the virtue of being close, and of preserving traces for an immense duration.

Translation? We're already collecting high-resolution imagery of the Moon's surface — why not scour it for signs of extraterrestrial influence? As a point of reference, the estimated cost of NASA's Curiosity mission (which, you'll recall, is charged with determining if Mars is, or ever was, hospitable to life) is 2.5 billion dollars. By comparison, Davies and Wagner say that crowd-sourced analyses of LRO imagery in search of alien artifacts could be readily expanded and outsourced at little to no extra cost.

In other words, if we were to find evidence of alien life in images already captured by the Orbiter (slim chances be damned), the ratio of impact to capital investment would dwarf that of pretty much every scientific endeavor in recent history. [Acto Astronautica]